Lincoln and religion has never been an easy subject. His parents and sister were all members of the Baptist faith, but he never joined. He was married by an Episcopal clergyman and his wife later became a Presbyterian, but did he not follow her. Though he frequently attended church services, he never seemed to prefer one denomination over another.
Throughout his presidency, Lincoln invoked the Almighty as often as any other American president, but his personal religious beliefs are difficult to pin down. When pressed on the issue, a friend commented, “I don’t know anything about Lincoln’s religion, nor do I think anybody else knows anything about it.”
Lincoln’s political opponents seized on the opportunity. The most striking example came in 1846, during Lincoln’s successful run for a seat in the U. S. Congress. His opponent was Rev. Peter Cartwright, a circuit-riding preacher who was famous for his stirring sermons and combative political speeches. The Methodist preacher used religion as a campaign issue. The folks in New Salem reported that Lincoln had been an infidel and many of his Springfield neighbors suggested that Lincoln was still counted among the unbelievers. A whispering campaign spread across central Illinois.
On this date in 1846, Lincoln confronted the “Charges of Infidelity” by issuing a handbill. Though he won the election by a vote of 6,340 to Cartwright’s 4,829, you can judge whether or not he clarified his personal religious beliefs. Here is the handbill in-full (CW, 1:382-383) :
July 31, 1846
To the Voters of the Seventh Congressional District.
A charge having got into circulation in some of the neighborhoods of this District, in substance that I am an open scoffer at Christianity,  I have by the advice of some friends concluded to notice the subject in this form. That I am not a member of any Christian Church, is true; but I have never denied the truth of the Scriptures; and I have never spoken with intentional disrespect of religion in general, or of any denomination of Christians in particular. It is true that in early life I was inclined to believe in what I understand is called the ``Doctrine of Necessity''---that is, that the human mind is impelled to action, or held in rest by some power, over which the mind itself has no control; and I have sometimes (with one, two or three, but never publicly) tried to maintain this opinion in argument. The habit of arguing thus however, I have, entirely left off for more than five years. And I add here, I have always understood this same opinion to be held by several of the Christian denominations. The foregoing, is the whole truth, briefly stated, in relation to myself, upon this subject.
I do not think I could myself, be brought to support a man for office, whom I knew to be an open enemy of, and scoffer at, religion. Leaving the higher matter of eternal consequences, between him and his Maker, I still do not think any man has the right thus to insult the feelings, and injure the morals, of the community in which he may live. If, then, I was guilty of such conduct, I should blame no man who should condemn me for it; but I do blame those, whoever they may be, who falsely put such a charge in circulation against me.
July 31, 1846. A. LINCOLN.
 Illinois Gazette, August 15, 1846. The handbill likewise appears in the Tazewell Whig, August 22, 1846.
 See Lincoln's letter to Allen Ford, August 11, 1846, infra.